Application of time delay spectrometry to medical imaging

Abstract

A medical ultrasonic imaging system based upon reflective mode time delay spectrometry (TDS) is being developed at JPL. The frequency is linearly swept from 1 to 10 MHz in 20 ms. The signals from the targets of interest are received at the transducer with a time delay proportional to range. In the TDS processing system the received and transmitted signals are coherently mixed to produce a difference signal in a lower frequency range. After detection and low‐pass filtering to remove unwanted higher frequency components, a fast Fourier transform (FFT) is used to convert the frequency components into a time display. The FFT processes the magnitude of the analytic signal to obtain an energy‐time curve. This curve is always positive and displays the time dependence of the total energy response of the received signal. A two‐dimensional image is constructed from a series of scan lines. Images produced using TDS have the higher range resolution and signal‐to‐noise ratios required for deep arterial imaging. [This ...